Matching the nutritional requirements to performance in broiler breeder hens.
Quantitative food restriction during the rearing and laying period has become the standard management procedure in commercial broiler breeder operations to control the rapid growth rate of broiler breeders. This raises problems with the amount of each nutrient to be supplied each day. Food allowances are manipulated according to the pattern of egg production. Birds are fed a generous allowance early in lay followed by a period of mild regulation over peak production and a subsequent reduction in allowance as egg production declines in the later part of lay. In the past little work has been done on developing the theory of determining the nutrient requirements of broiler breeders. Consequently, this generally accepted method of feeding these breeders is without a sound theoretical basis. The objective of this study was to address two aspects concerned with meeting the requirements of broiler breeder hens during the laying period, specifically in the later stages of lay. The first is the obesity in broiler breeders that results from an excessive intake of energy and leads to a decrease in egg production. The second is the rapid decline in egg production in ageing hens. Individual data were collected from broiler breeder hens in two experiments. The first to determine the extent to which broiler breeder hens could be made to utilize excess body lipid reserves whilst maintaining laying performance. The second to measure the responses to lysine at different ages and to determine if the efficiency of utilization of lysine changes at different ages. Results from the first experiment indicated that broiler breeders can utilize their body fat reserves as an energy source providing that their protein intake is sufficiently high and that they could maintain egg production for at least a limited period of time. Birds fed an energy intake of 1490 kJ ME/bird d and a protein intake of 25.8 g/bird d showed no decline in egg production compared to birds fed much higher energy intakes (1900 to 2000 kJ ME/bird d). It was concluded from this experiment that if birds become overfat at any stage in their productive lives this situation can possibly be rectified by feeding them diets with low energy contents. In the later stages of lay and on cold days birds can probably be fed energy intakes below their requirements with no detrimental effect on egg production. Results from the second experiment indicated that the efficiency of utilization of protein declines as broiler breeders age. The efficiency of utilization of lysine was significantly lower for birds of 53 and 65 weeks of age compared to birds of 31 and 42 weeks of age. This decline in efficiency with age was attributed to the fact that efficiency decreases when the rate of lay decreases to below 50%. There was therefore no indication that the protein requirements decrease as the laying year progresses although egg production declines. It was suggested that new methods of feeding broiler breeder hens later in lay be investigated because the present method of decreasing the food allowance at this time is probably not the most ideal way to achieve maximum performance.